The field of this invention relates to the seals which are used to seal between the casing hanger supporting casing in a wellhead and the wellhead in which the casing hanger is landed. The casing hanger and wellhead are used in the drilling and production of oil and gas from the formations of the earth, both on land and on the ocean floor.
A need has existed as oil and gas wells have been drilled into formations of progressively higher pressure and in deeper and deeper ocean waters for casing hangers which provide highly reliable metal to metal sealing between the casing hangers and wellhead. Additionally the casing hanger seal means needs to be protected from damage as it is travelling down thru a central riser pipe from the surface of the water to the mudline.
Several designs have been addressed to this area, most sharing the deficiencies of difficulties of unreliable sealing characteristics, difficulties in achieving a high enough pressure in the seal element to reliably seal against well bore pressures, service problems in retrieving the entire seal assembly when the seal has not sealed properly, and presetting of the seal going into the well bore.
The most common defect in the retrieval of the seals is that of the seal assemblies separating during the retrieval process as the top and the bottom of the seal assembly are connected in some cases only by rubber seal elements.